Recorded presentation10B.2
The summer North Atlantic Oscillation - past, present and future
Chris K. Folland, United Kingdom Meteorological Office, Exeter, Devon, United Kingdom; and H. Linderholm, J. Hurrell, S. Ineson, J. Knight, A. Scaife, and R. Eastman
Eigenvector analysis of mean sea level pressure data gives an North Atlantic Oscillation-like pattern in summer (SNAO) but whose spatial scale is somewhat smaller than in winter. Its southern node stretches from near UK to Scandinavia. Here we concentrate on July and August (high summer). When the southern node of the SNAO has higher pressure (positive SNAO), warmth, dryness and low cloudiness is seen. The SNAO varies strongly interannually in high summer, but also interdecadally. Regression analysis of the SNAO with sea surface temperature (SST) suggests that its interdecadal variations can be related in part to the Atlantic Multidecadal Oscillation. This is supported by Climate of the Twentieth Century integrations using the HadAM3 climate model. Because the SNAO strongly affects temperature and rainfall in Scotland and Scandinavia, paleoclimate data based on tree rings has been used to reconstruct an index of the SNAO back to the early eighteenth century. This has been checked against the 300 year long Central England temperature series. Finally, simulations with a version of the Hadley Centre coupled model HadGEM1 forced by enhanced concentrations of atmospheric carbon dioxide show a tendency for more positive values of the SNAO, amplifying the future effects of global warming in summer in North-west Europe. Recorded presentation
Session 10B, Climate of the 20th Century (C20C) Part III
Wednesday, 23 January 2008, 10:30 AM-12:00 PM, 217-218
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